Two-color squeezing and sub-shot-noise signal recovery in doubly resonant optical parametric oscillators

A monolithic doubly resonant optical parametric oscillator produced signal and idler modes at widely separated wavelengths whose amplitude fluctuations were correlated (53.6 1.0)% below the vacuum-noise level. The system was used to detect modulated signals well below the shot-noise limit. © 1990 The American Physical Society.